The objectives of this proposal are to investigate the associations between blood pressure and hypertensive end-organ injury in children. To test the hypothesis that abnormal circadian BP patterns in children are associated with hypertensive end-organ injury, 24-hour ambulatory BP monitoring (ABPM) will be performed and end-organ injury will be assessed by measuring: 1) left ventricular mass index by echocardiography, 2) carotid artery intima-media thickness by ultrasound, 3) microalbuminuria by 24-hour urine collection, and 4) retinal vasculopathy by digital retinal photography. To test the hypothesis that children who are referred by primary care providers for elevated casual blood pressure are representative of the overall population of hypertensive children, we will perform ABPM and end- organ injury assessment in two patient groups: unsolicited referrals to a pediatric hypertension program and case-identification by systematic school-based BP screening. School-based BP screening will be performed in approximately 10,000 children aged 12-16 in the Houston Independent School District by a team of nursing faculty and students. These groups will be compared with respect to demographics and clinical parameters derived from ABPM and the indices of end-organ injury. Current definitions of pediatric hypertension are based on population percentiles of casual BP measurements and not on the risk of hypertensive end-organ injury. Twenty-four hour ABPM provides a more complete and accurate representation of the daily circadian BP patterns and is superior to casual BP in the prediction of end-organ injury in adults. Few data exist on the relationship between ambulatory BP data and end-organ injury in children. A further barrier to the study of pediatric hypertension is the low prevalence of the condition, estimated at 1-2% of the pediatric population. This limitation has made adequate patient accrual difficult and predisposed studies to referral bias. The proposed studies will add significantly to our ability to practice evidence-based medicine regarding the evaluation and management of hypertensive children.